Octodon bridgesi

Octodon bridgesi, Bridges’s degu, belongs to the genus Octodon, in the family Octodontidae. Like the common degu, O. degus, it is a Chilean rodent.¹ Its name honours the botanist Thomas Bridges, who sent early specimens for identification.² It has a robust build, soft, thick fur and a brownish-grey coat with paler areas on the underside. It is listed as Vulnerable on the IUCN Red List.³ Much of its biology remains poorly documented.

Geographical distribution

Habitat alteration, including agricultural expansion, has reduced and fragmented its distribution in central Chile.⁴ Historical records extend through Maule, Biobío and Araucanía, including Nahuelbuta and parts of the Andes, with records near Curicó and from sea level to approximately 1,200 m. Gaps in records make precise limits difficult to establish.³

Older accounts also reported O. bridgesi in Argentina, including Lanín National Park. Those Argentine populations, together with populations in neighbouring parts of Chile, were subsequently described as O. ricardojeda. Historical distribution and ecological records must therefore be interpreted in the light of that revision.⁸

Ecology

Habitat

Rather than being a habitual burrow excavator, Bridges’s degu uses natural shelters and constructs nests among shrubs, dry grasses, bamboo or spaces beneath rocks. It occupies wooded areas, shrubland, clearings and Andean valleys, where dense vegetation provides cover.

Plants recorded in its habitat include Aristotelia chilensis, Lithraea caustica, Peumus boldus, Gevuina avellana, Escallonia pulverulenta, Ugni molinae and Teline monspessulana. Some habitat plants also contribute to its diet. In the Biobío basin, records include forests containing Nothofagus dombeyi, Araucaria araucana and Nothofagus pumilio, as well as Pinus radiata plantations and sclerophyllous scrub. It favours dense shrubs interspersed with open ground, often with relatively low tree density.⁵

Other rodents recorded in the same broad habitats include O. degus, chinchilla rats such as Abrocoma bennetti, Spalacopus cyanus, Aconaemys fuscus and Lagidium viscacia. These are associated species, rather than parasites.

Predators and threats

Predators include barn owls, the kodkod (Leopardus guigna) and the culpeo fox (Lycalopex culpaeus). In one local barn-owl diet study summarised by the Chilean environment ministry, the degu accounted for approximately 11.1% of prey in spring–summer and 5.3% in autumn–winter. Archaeological evidence also indicates human consumption approximately 4,460–1,520 years before present, rather than those dates before the Common Era.⁵

Introduced black rats (Rattus rattus), European rabbits (Oryctolagus cuniculus) and domestic goats (Capra hircus) can affect its habitat and resources.

Activity and social organisation

Laboratory studies and field observations describe predominantly nocturnal activity.⁶⁷ This pattern should not automatically be applied to O. lunatus, which has been observed to be active both by day and by night. Bridges’s degu climbs trunks and vegetation to feed. In the studied pine-plantation habitat, Pinus radiata needles and tissues were important dietary components.⁵

Population densities reported from one local study averaged approximately eight animals per hectare, falling to around 2–8 in winter and summer and reaching 16–18 in spring and autumn. These local figures are not universal species-wide values and do not by themselves measure sociability. Females have reproductive cycles broadly comparable to those of O. degus; the small number examined in the cited study had litters of two or three young.⁵

Sources

Woods, C. A., & Boraker, D. K. (1975). Octodon degus. Mammalian Species, 67, 1–5. https://doi.org/10.2307/3503820

Palma, R. E. (2007). Estado actual de la mastozoología en Chile. Mastozoología Neotropical, 14(1), 5–9. https://mn.sarem.org.ar/article/estado-actual-de-la-mastozoologia-en-chile/

IUCN (n.d.). Octodon bridgesi. The IUCN Red List of Threatened Species. https://www.iucnredlist.org/species/15087/115124772

SAAVEDRA, BÁRBARA & SIMONETTI, JAVIER A (2003). Holocene distribution of Octodontid rodents in central Chile. Revista chilena de historia natural, 76(3), 383–389. https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-078X2003000300004&lng=en&nrm=iso&tlng=en

Ministerio del Medio Ambiente de Chile (2015). Ficha de antecedentes de especie: Octodon bridgesi. 12.º proceso de clasificación de especies. https://clasificacionespecies.mma.gob.cl/wp-content/uploads/2019/10/Octodon_bridgesi_12RCE_FIN.pdf

Ocampo-Garcés, A., et al. (2005). Wheel-running and rest activity pattern interaction in two octodontids (Octodon degus, Octodon bridgesi). Biol Res, 38(2-3), 299-305. https://doi.org/10.4067/s0716-97602005000200019

OCAMPO-GARCÉS, ADRIÁN, et al. (2006). Circadian chronotypes among wild-captured west Andean octodontids. Biological Research, 39(2), 209–220. https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602006000200003&lng=en&nrm=iso&tlng=en

D’Elía, G., Teta, P., Verzi, D. H., Cadenillas, R., & Patton, J. L. (2021). A new living species of degu, genus Octodon (Hystricomorpha: Octodontidae). Journal of Mammalogy, 102(1), 139–154. https://doi.org/10.1093/jmammal/gyaa143